Nitride compound semiconductor element and production method therefor

ABSTRACT

A nitride compound semiconductor element according to the present invention is a nitride compound semiconductor element including a substrate  1  having an upper face and a lower face and a semiconductor multilayer structure  40  supported by the upper face of the substrate  1,  such that the substrate  1  and the semiconductor multilayer structure  40  have at least two cleavage planes. At least one cleavage inducing member  3  which is in contact with either one of the two cleavage planes is provided, and a size of the cleavage inducing member  3  along a direction parallel to the cleavage plane is smaller than a size of the upper face of the substrate  1  along the direction parallel to the cleavage plane.

TECHNICAL FIELD

The present invention relates to a nitride compound semiconductorelement and a production method therefor.

BACKGROUND ART

A band gap of a nitride compound semiconductor whose composition isexpressed by the general formula In_(x)Ga_(y)Al_(z)N (where x+y+z=1,0≦x≦1, 0≦y≦1, 0≦z≦1) may have a width corresponding to blue light orultraviolet light through adjustment of the mole fraction of eachelement. Therefore, there have been vigorous research activitiesdirected to light-emitting devices, e.g., semiconductor lasers, thatcomprise a nitride compound semiconductor as an active layer.

FIG. 1 shows the crystal structure of a nitride compound semiconductor.As shown in FIG. 1, a nitride compound semiconductor has a crystalstructure of a hexagonal-system. Therefore, when fabricating asemiconductor laser which is constructed so that its upper face(principal face) is the (0001) plane and its resonator end faces are theM-plane (1-100), cleavage is likely to occur not along an A-plane whichis perpendicular to these planes, but along a crystal plane which istilted by 30° from the A-plane. As a result, there is a problem in that,not only when performing cleavage along the A-plane, but also whenforming cleavage along the M-planes (1-100) to form the resonator endfaces, cracks are likely to occur in a direction which is tilted by 60°from the M-plane (1-100).

Due to this problem, it has conventionally been very difficult tofabricate a nitride compound semiconductor element having smoothresonator end faces.

Note that a sapphire substrate, which has conventionally been widelyused as a substrate for nitride compound semiconductor elements, is notcapable of cleaving. Therefore, when forming a semiconductor laserhaving a sapphire substrate, it has been practiced to perform scribingalong the M-plane from the side of a nitride compound semiconductorlayer that is grown on a sapphire substrate to thus form a scratch inthe nitride compound semiconductor layer, this being an attempt tofacilitate the formation of a cleavage plane.

Patent Document 1 discloses a method which involves performing an edgescribing for a nitride compound semiconductor layer, and thereafterperforming a cleavage through breaking.

[Patent Document 1] Japanese Laid-Open Patent Publication No.2000-058972

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, according to the aforementioned conventional technique, sincescratches are formed in the nitride compound semiconductor layer throughscribing or dicing, there is a problem in that “burrs”, “chipping”,“end-face cracks” and the like are likely to occur, thus resulting in areduced production yield. There is also a problem in that, since theactive layer is likely to suffer from strain and crystal defects,scratches and ruggednesses may occur in a resonator end face(light-outgoing surface), thus deteriorating the optical characteristicsand reliability.

Furthermore, when a lateral crystal growth layer with a reduced defectdensity is formed on a substrate, the substrate may not be reached by ascratch even if an edge scribing is performed from the nitride compoundsemiconductor layer side. Moreover, an air gap and an insulative filmlayer which exist between the lateral crystal growth layer and thesubstrate are fragile regions with a low mechanical strength, andtherefore are likely to experience crystal peeling and may be damaged.Therefore, especially in the case of growing a lateral crystal growthlayer on a substrate, it has been difficult with the conventional methodto obtain good resonator surfaces.

The present invention has been made in order to solve the aforementionedproblems, and a main objective thereof is to provide a nitride compoundsemiconductor element which allows cleavage to be performed with a goodyield, and a production method therefore.

Means for Solving the Problems

A nitride compound semiconductor element according to the presentinvention is a nitride compound semiconductor element including asubstrate having an upper face and a lower face and a semiconductormultilayer structure supported by the upper face of the substrate, suchthat the substrate and the semiconductor multilayer structure have atleast two cleavage planes, comprising: at least one cleavage inducingmember which is in contact with either one of the two cleavage planes,wherein a size of the cleavage inducing member along a directionparallel to the cleavage plane is smaller than a size of the upper faceof the substrate along the direction parallel to the cleavage plane.

In a preferred embodiment, the upper face of the substrate has arectangular shape, and the cleavage member is positioned in at least oneof four corners of the upper face of the substrate.

In a preferred embodiment, the semiconductor multilayer structure has alaser resonator structure in which the cleavage planes function asresonator end faces; and a size of the cleavage inducing member along aresonator length direction is half or less of the resonator length.

In a preferred embodiment, the cleavage inducing member is smaller thana 180 μm×50 μm rectangle.

In a preferred embodiment, two or more cleavage inducing members arecomprised, and arranged along a resonator length direction; and aninterval between adjoining cleavage inducing members along the resonatorlength direction is 80% or more of the resonator length.

In a preferred embodiment, the cleavage inducing member is composed of amask layer which is formed on the upper face of the substrate or in thesemiconductor multilayer structure.

In a preferred embodiment, the cleavage inducing member is composed of agap which is formed in the semiconductor multilayer structure.

In a preferred embodiment, a trench is formed on the upper face of thesubstrate; and the mask layer is positioned above the trench.

In a preferred embodiment, the mask layer is composed of a materialwhich suppresses crystal growth of semiconductor layers composing thesemiconductor multilayer structure.

In a preferred embodiment, the mask layer is formed of at least onematerial selected from the group consisting of: an oxide or nitride ofsilicon, aluminum, titanium, niobium, zirconia, or tantalum; gold;platinum; aluminum; nickel; palladium; and titanium.

In a preferred embodiment, the cleavage inducing members are located onboth sides of a laser optical waveguide portion in the semiconductormultilayer structure.

In a preferred embodiment, the semiconductor multilayer structureincludes: an n-type nitride compound semiconductor layer and a p-typenitride compound semiconductor layer; and an active layer interposedbetween the n-type nitride compound semiconductor layer and the p-typenitride compound semiconductor layer.

In a preferred embodiment, the substrate is a nitride compoundsemiconductor.

In a preferred embodiment, a pair of electrodes are formed on the upperface and the lower face of the substrate.

A production method for a nitride compound semiconductor elementaccording to the present invention is a production method for a nitridecompound semiconductor element including a substrate having an upperface and a lower face and a semiconductor multilayer structure supportedby the upper face of the substrate, comprising: a step of providing awafer to be split into the substrate; a step of growing semiconductorlayers composing the semiconductor multilayer structure on the wafer;and a step of performing cleavage of the wafer and the semiconductormultilayer structure to form a cleavage plane of the semiconductormultilayer structure, further comprising a step of arranging a pluralityof cleavage inducing members at positions where the cleavage plane is tobe formed.

In a preferred embodiment, the step of arranging the cleavage inducingmembers includes: a step of depositing an insulative film; and a step ofpatterning the insulative film to form a plurality of mask layers beingarranged along a line and defining positions at which the resonator endfaces are to be formed.

In a preferred embodiment, the mask layers are formed on a principalface of the wafer.

In a preferred embodiment, the mask layers are formed in thesemiconductor multilayer structure.

Effects of the Invention

According to the present invention, since cleavage is induced along acleavage inducing member, the problem of cracks being likely to occur ina 60° direction with respect to the M-plane in relation to cleavage of ahexagonal-system nitride compound semiconductor is solved, thusfacilitating the formation of smooth resonator end faces.

Moreover, according to the present invention, burrs, chipping, scratchesand ruggednesses in the resonator end faces, strain in the active layer,formation of crystal defects and the like, which are likely to occurupon cleavage, are suppressed. Therefore, there is provided an effectthat the optical characteristics and electrical characteristics of thefinally-obtained semiconductor laser are improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A perspective view showing crystal plane orientations of anitride compound semiconductor.

FIG. 2 (a) to (e) are step-by-step cross-sectional views showingformation of mask layers according to Embodiment 1 of the presentinvention and a production method for a nitride compound semiconductormultilayer structure 40.

FIG. 3 (a) and (e) are cross-sectional views showing a relationshipbetween mask layers according to Embodiment 1 of the present inventionand the nitride compound semiconductor multilayer structure 40.

FIG. 4 A schematic diagram showing a wafer on which mask layersaccording to Embodiment 1 of the present invention are periodicallyarranged.

FIG. 5 A plan view showing the shape of mask layers according toEmbodiment 1 of the present invention.

FIG. 6 (a) is a plan view showing a wafer on which mask layers accordingto Embodiment 1 of the present invention are periodically arranged; and(b) is a plan view showing a split semiconductor laser.

FIG. 7 (a) to (i) are step-by-step cross-sectional views showing aprocess in which a nitride compound semiconductor element according toEmbodiment 1 of the present invention is processed.

FIG. 8 A schematic diagram showing a method of separation for nitridecompound semiconductor elements according to Embodiment 1 of the presentinvention.

FIG. 9 A plan view showing a laser bar, formed through primary cleavage,according to Embodiment 1 of the present invention.

FIG. 10 A schematic diagram showing a nitride compound semiconductorelement, after secondary cleavage, according to Embodiment 1 of thepresent invention.

FIG. 11 An upper plan view showing a manner in which the nitridecompound semiconductor element according to Embodiment 1 of the presentinvention is packaged.

FIG. 12 (a) and (b) are schematic diagrams showing a primary cleavage ofa nitride compound semiconductor element according to a comparativeexample against Embodiment 1 of the present invention.

FIG. 13 (a) to (i) are step-by-step cross-sectional views showing aproduction method according to Embodiment 2 of the present invention.

FIG. 14 A view showing the construction of a GaN wafer 1 according toEmbodiment 3 of the present invention.

FIG. 15 A view showing the construction of the GaN wafer 1 according toEmbodiment 3 of the present invention.

FIG. 16 A view showing a nitride compound semiconductor elementaccording to Embodiment 4 of the present invention.

FIG. 17 (a), (b) and (c) are plan views showing mask layers (cleavageinducing members) of different shapes.

FIG. 18 An optical micrograph of a cleavage plane in which an end-facecrack is formed.

FIG. 19 An optical micrograph showing a cross section of a sample inwhich a thick epitaxially-grown layer is formed in a region near themask layer.

FIG. 20 An optical micrograph showing a cleavage which has deviated froma row of mask layers of a rectangular shape.

FIG. 21 (a) is a plan view schematically showing a cleavage in the casewhere the easily-cleavable direction of a crystal has deviated from acleavage inducing member extending in the form of a stripe; and (b) is aplan view schematically showing a cleavage where the easily-cleavabledirection of a crystal has deviated from a direction in which thecleavage inducing members are intermittently arranged.

DESCRIPTION OF THE REFERENCE NUMERALS

1 . . . wafer3 . . . cleavage inducing member (mask layer)18 . . . optical waveguide23 . . . p-side wiring24 . . . n-side wiring27 . . . trench30 . . . high defect-density region40 . . . semiconductor multilayer structure

BEST MODE FOR CARRYING OUT THE INVENTION

A nitride compound semiconductor element according to the presentinvention includes a substrate having an upper face and a lower face,and a semiconductor multilayer structure which is supported by the upperface of the substrate, such that the substrate and the semiconductormultilayer structure have at least two cleavage planes.

In the present invention, “cleavage inducing members” are provided inorder to facilitate “cleavage” of a crystal during its production steps.Therefore, in most of the semiconductor elements that are finallyfabricated, (at least a portion of) a cleavage inducing member(s)exists. Each cleavage inducing member in each semiconductor element isin contact with either one of two cleavage planes. In other words, thecleavage inducing member according to the present invention is not sizedso as to extend from one of two parallel cleavage planes to the other.The size of the cleavage inducing member along a direction parallel to acleavage plane is smaller than the size of an upper face of thesubstrate along the direction parallel to the cleavage plane. In otherwords, the cleavage inducing member according to the present inventionis sized so as to be in contact with a portion of a cleavage plane, anddoes not extend from end to end on the cleavage plane along the lateraldirection.

Hereinafter, with reference to the drawings, a first embodiment of thenitride compound semiconductor element according to the presentinvention will be described. The nitride compound semiconductor elementaccording to the present invention is preferably a semiconductor laserwhose cleavage planes are utilized as resonator end faces, but may beany other light-emitting device, e.g., an LED (Light Emitting Diode), ora transistor. Although a semiconductor element other than asemiconductor laser does not utilize its cleavage planes as resonatorend faces, the ability to separate a hard nitride compound into chipswith a good yield through cleavage produces advantages such asfacilitated production.

Embodiment 1

First, with reference to FIG. 2( a) to FIG. 2( e), a production methodfor the nitride compound semiconductor laser according to the presentembodiment will be described. FIG. 2( a) to FIG. 2( e) are partialcross-sectional views during important steps. In actuality, theillustrated portion is merely a part of a wafer which is sized with adiameter of about 50 mm.

As shown in FIG. 2( a), a GaN wafer 1 whose upper face is the (0001)plane is provided, and a photoresist film 2 is applied on the upper faceof the GaN wafer 1. Note that the cross section of the GaN wafer 1 thatis shown in FIG. 2( a) to FIG. 2( d) is the M(1-100) plane, which willbe exposed through primary cleavage. The <11-20> direction lies in theplane of the figure, and is parallel to the upper face (0001) of the GaNwafer 1.

By subjecting the photoresist film 2 to exposure and development througha known photolithography step, the photoresist film 2 is patterned asshown in FIG. 2( b). The patterned photoresist film 2 has a plurality ofopenings 2′ which are periodically arranged in row and columndirections. The shapes, sizes, and positions of the openings 2′ can bearbitrarily set by changing the design of a photomask which is used forthe exposure in a photolithography step. In the present embodiment, thelocation of the openings 2 is determined so as to define the “cleavageinducing members 3” shown in FIG. 4. The details of the constructionshown in FIG. 4 will be described later.

Next, as shown in FIG. 2( c), a silicon dioxide (SiO₂) film 3′ isdeposited on the photoresist mask 2. Although the silicon dioxide film3′ is mostly positioned on the photoresist mask 2, some portions thereofare in contact with the upper face of the GaN wafer 1 through theopenings 2′. Deposition of the silicon dioxide film 3′ may be performedby an ECR sputtering technique, for example. Thereafter, a lift-off isperformed by removing the photoresist film 2 with an organic solutionsuch as acetone, thus forming the cleavage inducing member 3 of silicondioxide as shown in FIG. 2( d).

Next, a multilayer structure 40 of nitride compound semiconductor isformed on the GaN wafer 1 having the plurality of cleavage inducingmembers 3 periodically arranged on its upper face. In the presentembodiment, a metal-organic vapor phase epitaxy (MOVPE) technique isused to grow layers of nitride compound semiconductor expressed asIn_(x)Ga_(y)Al_(z)N (where x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1). Specifically,the semiconductor multilayer structure 40 as shown in FIG. 2( e) isformed on the GaN wafer 1.

Hereinafter, with reference to FIG. 2( e), production steps of thesemiconductor multilayer structure 40 of the present embodiment will bedescribed.

First, the GaN wafer 1 having the cleavage inducing members 3 formed onits upper face is retained on a susceptor in a reactor of MOVPEequipment. Then, the reactor is heated to about 1000° C., and sourcegases, i.e., trimethylgallium (TMG) supplied in an amount of 7 s ccm andammonia (NH₃) gas supplied in an amount of 7.5 slm, and a carrier gas ofhydrogen are simultaneously supplied, and silane (SiH₄) gas is suppliedas an n-type dopant, thus allowing an n-type GaN layer 10 having athickness of about 1 μm and an Si impurity concentration of about 1×10¹⁸cm⁻³ to grow.

At this time, no growth of n-type GaN crystal directly occurs in theregions of the upper face of the GaN wafer 1 that are covered by thecleavage inducing members 3. However, the n-type GaN which has grownfrom the regions of the upper face of the GaN wafer 1 that are notcovered by the cleavage inducing members 3 grows across the surface ofthe cleavage inducing members 3 in the lateral direction. Therefore, thesurface of the cleavage inducing members 3 is also covered by the n-typeGaN layer 10.

Thereafter, while also supplying trimethylaluminum (TMA), an n-typecladding layer 11 composed of n-type Al_(0.05)Ga_(0.95)N with athickness of about 1.5 μm and an Si impurity concentration of about5×10¹⁷ cm⁻³ is grown. Then, after growing a first optical guide layer 12composed of n-type GaN with a thickness of about 120 nm and an Siimpurity concentration of about 1×10¹⁸ cm⁻³, the temperature is loweredto about 800° C., the carrier gas is switched from hydrogen to nitrogen,and trimethylindium (TMI) and TMG are supplied, thus growing quantumwells (three layers) composed of In_(0.1)Ga_(0.9)N with a film thicknessof about 3 nm and a multi-quantum well active layer 13 composed ofIn_(0.02)Ga_(0.98)N barrier layers (two layers) with a film thickness ofabout 9 nm.

The temperature within the reactor is again elevated to about 1000° C.,the carrier gas is switched back from nitrogen to hydrogen, and whilesupplying a p-type dopant of biscyclopentadienylmagnesium (Cp₂Mg) gas, acapping layer 14 composed of p-type Al_(0.15)Ga_(0.85)N with a filmthickness of about 10 nm and an Mg impurity concentration of about5×10¹⁷ cm⁻³ is grown.

Next, a second optical guide layer 15 composed of p-type GaN with athickness of about 120 nm and an Mg impurity concentration of about1×10¹⁸ cm⁻³ is grown. Thereafter, a p-type cladding layer 16 composed ofp-type Al_(0.05)Ga_(0.9)N with a thickness of about 0.5 μm and animpurity concentration of about 5×10¹⁷ cm⁻³ is grown. Finally, a p-typecontact layer 17 composed of p-type GaN with a thickness of about 0.1 μmand an Mg impurity concentration of about 1×10¹⁸ cm⁻³ is grown.

Note that, by adjusting the crystal growth conditions for the n-type GaNlayer 10 and other semiconductor layers, it may be possible to leave thesurface of the cleavage inducing members 3 exposed, rather than beingcompletely covered. FIG. 3( a) shows a semiconductor multilayerstructure 40 which is formed under conditions such that no crystalgrowth occurs on the cleavage inducing members 3.

Although FIG. 2( e) illustrates the n-type GaN layer 10 as having a flatupper face, it is usually the case that ruggednesses are formed on theupper face of the n-type GaN layer 10 in accordance with thepresence/absence of the cleavage inducing members 3. In extreme cases,as described above, the n-type GaN layer 10 may locally have a zerothickness above the cleavage inducing members 3. Moreover, it would alsobe possible to form the n-type GaN layer 10 on the cleavage inducingmembers 3 so as to have a thickness substantially equal to the thicknessof its portions in the other regions.

In the example shown in FIG. 2( e), portions 30 (hereinafter referred toas “high defect-concentration regions”) of the semiconductor multilayerstructure 40 that are positioned immediately above the cleavage inducingmembers 3 have a relatively deteriorated crystallinity. Thus, due to thepresence of the cleavage inducing members 3 and the highdefect-concentration regions 30, there is local stress occurring in thesemiconductor multilayer structure 40 which has grown on the GaN wafer1. It is considered that such local large stress, occurring in lines,makes it easy to induce cleavage in predetermined directions.

The cleavage inducing members 3 do not need to be formed directly on theupper face of the wafer 1, but may be formed on any layer among thesemiconductor layers 10 to 16 shown in FIG. 2( e). FIG. 3( b)schematically shows an example where the cleavage inducing members 3 arelocated within the semiconductor multilayer structure 40.

Thus, according to the present embodiment, periodic strain can begenerated in the semiconductor multilayer structure 40 because of thearrangement of the cleavage inducing members 3. However, if thethickness of the cleavage inducing members 3 is too large, the activelayer may also have a large strain due to their influence. In order toensure that such strain does not become too large, the thickness of thecleavage inducing member 3 may be reduced to 0.5 μm or less.

However, depending on the shapes and positions of the cleavage inducingmembers 3, their thickness may be set to a value exceeding 0.5 μm. Inparticular, as shown in FIGS. 3( a) and (b), in the case where thecleavage inducing members 3 are not covered by semiconductor but insteadappear exposed when seen from above the semiconductor multilayerstructure 40, the thickness of the cleavage inducing members 3 may bearbitrary.

Hereinafter, with reference to FIG. 4, the construction of the cleavageinducing members 3 will be specifically described.

The cleavage inducing members 3 according to the present embodiment areperiodically arranged along the <11-20> direction, in a manner not tointersect any optical waveguide forming regions 18′ which are formed inthe semiconductor multilayer structure 40. The distance between twoadjoining cleavage inducing members 3 along the <11-20> direction is setto be substantially the same value as the size along the <11-20>direction of the finally-obtained laser device. In the presentembodiment, the size along the <11-20> direction of each laser device isabout 400 μm, and therefore the arraying pitch of the cleavage inducingmembers 3 along the <11-20> direction is also set at 400 μm.

On the other hand, the arraying pitch of the cleavage inducing members 3along the <1-100> direction is set at a value which is equal to theresonator length of each laser device. In the present embodiment, theresonator length is about 600 μm, and therefore the arraying pitch ofthe cleavage inducing members 3 along the <1-100> direction is also setat about 600 μm.

The planar shape of each cleavage inducing member 3 is square (size: 10μm×10 μm), for example. Thus, by arranging, along lines 25 and lines 26on the wafer 1, the cleavage inducing members 3 which are sufficientlysmall relative to the size of each laser device, it becomes possible toperform primary and secondary cleavages at accurate positions. Thecleavage inducing members 3 only need to be arranged in positions wherecleavage is to be induced (i.e., the lines 25 and lines 26), and they donot need to be arranged with a constant period. However, since they arepreferably located so as to avoid the optical waveguide forming regions18′, it is preferable to place them in a periodical arrangement.

Since the primary cleavage is to take place along the <11-20> directionso as to expose the (1-100) plane as a cleavage plane, it is preferablethat the size of the cleavage inducing members 3 along the <1-100>direction is sufficiently small relative to the resonator length. Thereason is that, if the size of the cleavage inducing members along the<1-100> direction is too large, it becomes difficult to define theposition (position along the <1-100> direction) of the cleavage plane.Therefore, the size of the cleavage inducing members 3 along the <1-100>direction should be half or less of the resonator length, and ispreferably 20% or less of the resonator length. The absolute value ofthis size is preferably 150 μm or less, and more preferably 50 μm orless.

On the other hand, the size of the cleavage inducing members 3 along the<11-20> direction may be relatively larger than its size along the<1-100> direction. The size of the cleavage inducing members 3 along the<11-20> direction is to be determined from the standpoint of ensuringcleavage inducing effects while also reducing the strain occurring inthe optical waveguide and the defect density. Therefore, it ispreferable that the size of the cleavage inducing members 3 along the<11-20> direction is 5 μm or more, and is smaller than a value obtainedby subtracting the width of the waveguide (i.e., size along the <11-20>direction) from the size along the <11-20> direction of the laserdevice. The typical size of the cleavage inducing members 3 along the<11-20> direction is no less than 5 μm and no more than 180 μm.

FIG. 5 shows a preferable example of the planar shape of the cleavageinducing members 3. As shown in FIG. 5, when each cleavage inducingmember 3 has a longitudinal axis along the <11-20> direction, with itsboth ends being pointed so as to constitute acute angles, it is easy tosuppress occurrence of cracks along a direction which is deviated by 60°from the <11-20> direction. Note that the shapes and locations of thecleavage inducing members 3 are not to be limited to the above example.

Note that each line 25 shown in FIG. 4 is defined by a row of pluralcleavage inducing members 3 which are arranged along the <11-20>direction, and primary cleavage is to take place along these lines 25.Therefore, it is preferable to set the arraying pitch of the cleavageinducing members 3 along the <1-100> direction to be equal to theresonator length, but the arraying pitch of the cleavage inducingmembers 3 along the <11-20> direction is not constrained by the size ofthe laser device. In other words, so long as the cleavage inducingmembers 3 are on the lines 25 and located in regions other than theoptical waveguide forming regions 18′, they do not need to be arrangedalong the <11-20> direction with a constant period, as described above.

FIG. 6 schematically shows the construction of chips to be split from awafer through primary cleavage and secondary cleavage. FIG. 6( a) showsa state before the split, whereas FIG. 6( b) shows one of the individualsplit-chips.

In the example shown in FIG. 6( b), cleavage is occurring at a positiontraversing the cleavage inducing members 3. However, the cleavage planedoes not need to traverse the cleavage inducing members 3, but mayinstead be formed near the cleavage inducing members 3. As shown in FIG.6( b), if primary and secondary cleavages occur so as to traverse thecleavage inducing members 3, each finally-obtained semiconductor laserchip will include four broken pieces of cleavage inducing members 3 atits four corners. However, it is not necessary for each semiconductorlaser to contain four broken pieces of cleavage inducing members 3 atits four corners. Depending on the cleavage position, the number of(broken pieces or whole) cleavage inducing members 3 to be contained ineach semiconductor laser may fluctuate.

In extreme cases, a given semiconductor laser may finally contain nocleavage inducing member 3 at all. In such cases, a semiconductor laseradjoining that semiconductor laser may contain at least one cleavageinducing member 3 which has been left unbroken.

The material of the cleavage inducing members 3 is not limited to SiO₂,but may be an insulator such as silicon nitride. Preferably, they areformed of at least one material selected from the group consisting of:an oxide or nitride of silicon, aluminum, titanium, niobium, zirconia,or tantalum; gold; platinum; aluminum; nickel; palladium; and titanium.

The cleavage inducing members 3 may be what can cause selective growthof the nitride compound semiconductor which is stacked in layers so asto compose a laser structure, and may not only be an insulator but alsoa metal. Moreover, they may be semiconductors of different compositionsin accordance with the nitride compound semiconductor crystal to begrown. Moreover, the cleavage inducing members 3 may be modifiedportions obtained by, e.g. implanting ions into the nitride compoundsemiconductor crystal layer. For example, if an aluminum gallium nitride(Al_(x)Ga_(y)N: where x+y=1, 0≦x≦1, 0≦y≦1) whose aluminum componentdiffers from that of the nitride compound semiconductor crystal to bestacked is used for the cleavage inducing members 3, a difference instress occurs at the interfaces because the nitride compoundsemiconductor crystal and the Al_(x)Ga_(y)N mask layer have differentcoefficients of thermal expansion, thus allowing the cleavages in thesubsequent steps to progress more easily. It is preferable that theAl_(x)Ga_(y)N mask layer has a large Al mole fraction. The greater theAl mole fraction of the Al_(x)Ga_(y)N mask layer is, the greatercoefficient of thermal expansion will exist in the c-plane, so that agreater difference in stress can be obtained.

Hereinafter, with reference to FIG. 7( a) to FIG. 7( i), an embodimentof a method for fabricating a semiconductor laser from the wafer 1 onwhich the semiconductor multilayer structure 40 of FIG. 2( e) is formedwill be described.

First, as shown in FIG. 7( a), after an insulating layer 19 is formed onthe upper face of the semiconductor multilayer structure 40, aphotoresist film 20 is applied thereon. Next, an exposure anddevelopment of the photoresist film 20 is performed in aphotolithography step, thus forming a resist mask 20′ as shown in FIG.7( b). The resist mask 20′ has a stripe pattern defining the opticalwaveguide forming regions 18′ shown in FIG. 4. By using a hydrofluoricacid solution to etch portions of the insulative film 19 that are notcovered by the resist mask 20′, the upper face (p-type contact layer 17)of the semiconductor multilayer structure 40 is exposed as shown in FIG.7( c).

After removing the resist mask 20′ as shown in FIG. 7( d), as shown inFIG. 7( e), portions of the upper portion of the semiconductormultilayer structure 40 that are not covered by the insulating layer 19′are etched. This can be carried out by loading the wafer 1 into a dryetching apparatus and performing an anisotropic dry etching. Anisotropicetching is to be performed until portions of the p-type semiconductorlayer that are positioned above the active layer (leftovers) reach athickness of about 100 nm.

Thereafter, the insulating layer 19′ is removed as shown in FIG. 7( f),whereby ridge-shaped optical waveguides 18 are formed which are composedof the p-type contact layer 17 and the Al_(0.05)Ga_(0.95)N claddinglayer 16. The direction in which the optical waveguides 18 extend is<1-100>.

Next, as shown in FIG. 7( g), after regions other than the regions wheren-type electrodes are to be formed are covered by an insulative film 21which is composed of SiO₂, a dry etching is performed to expose then-type contact layer. By removing the insulative film 21, a structureshown in FIG. 7( h) is obtained.

Next, as shown in FIG. 7( i), after depositing an insulative film 22 foreffecting electrical separation between the p-side and the n-side,portions of the insulative film 22 that are positioned on the p-typecontact layer are removed with a hydrofluoric acid solution. Thereafter,n-side electrodes 23 and p-side electrodes 24 are sequentially formed inportions where the insulative film 22 has been removed. Each n-sideelectrode 23 has a structure in which molybdenum (Mo), platinum (Pt),and gold (Au) are stacked, for example. Each p-side electrode 24 has astructure in which palladium (Pd), Pt, and Au are stacked, for example.

Hereinafter, with reference to FIG. 8 to FIG. 10, cleavage and packagingsteps will be specifically described.

First, the rear face of the GaN wafer 1 is polished, and the overallthickness of the semiconductor multilayer structure 40 and the wafer 1is reduced to about 100 μm. Next, by using an apparatus which is notshown, stress is applied to effect a primary cleavage along the lines 25shown in FIG. 8. At this time, the stress occurring at the interfacesbetween the cleavage inducing members 3 and the nitride compoundsemiconductor layer is released, so that a cleavage along the cleavageinducing members 3, which are arranged along the <11-20> direction, isinduced. As a result, crack occurrence in the 60° direction issuppressed, so that laser bars having smooth resonator end faces of theM-plane (1-100) are fabricated. Thus, according to the presentembodiment, the presence of the cleavage inducing members 3 makes itdifficult for disruption of the laser bars due to the aforementionedcracks to occur. As a result, it is possible to make long laser bars,reduce the production cost, and improve the yield.

Next, after a multilayered dielectric film composed of SiO_(x) andTiO_(x) is formed on both or either one of the resonator end faces ofeach laser bar (FIG. 9) obtained through the primary cleavage, asecondary cleavage is performed along the lines 26, whereby laser chips(individual semiconductor lasers) shown in FIG. 10 are separated fromeach laser bar. Each semiconductor laser includes as its substrate achip which has been split from the GaN wafer 1.

Next, via solder, each semiconductor laser is placed in such a mannerthat its p-side portion is in contact with the upper face of a heat sink28 which is composed of silicon carbide (SiC), and wiring is performedvia wire bonding. At this time, by taking advantage of the cleavageinducing members 3 being in specific positions of the laser device, thecleavage inducing members 3 can exhibit a function as positioningmarkers during the packaging step.

As shown in FIG. 11, it is preferable to perform soldering in such amanner that the laser device protrudes from the upper face of the heatsink 28 in the <1-100> direction. In the example shown in FIG. 11, thecleavage inducing members 3 which are located at the optical output endface stick out from the heat sink 28 in the lateral direction. With suchlocation, solder becomes unlikely to adhere to the light-outgoingsurface, and contamination of the optical output end faces issuppressed, whereby the packaging yield is improved.

The laser device which has been produced by the above method has smoothresonator surfaces. At room temperature, continuous oscillation wasconfirmed at an operating current of 60 mA, with a threshold current of30 mA and an output power of 50 mW, and a lifespan of 1000 hours or morewas exhibited.

Moreover, in the laser device of the present embodiment, since tensilestress is released near the cleavage inducing members 3, a “windowstructure region” which has a relatively large band gap and in whichlight absorption is suppressed is formed near the resonator end faces.As a result, light emission at a high output power becomes possible.Note that, as the distance between each cleavage inducing member 3 andthe ridge becomes shorter, the stress releasing effects will beenhanced, but the possibility of defects being introduced at thelight-outgoing surface will also increase. Therefore, the distancebetween each cleavage inducing member 3 and the ridge stripe is to beset within a range from 2 to 50 μm, e.g. about 5 μm.

Although cleavage is also performed along the lines 26 in the aboveexample, the faces other than the resonator end faces do not need to becleavage planes. Therefore, cutting with laser, etc., may be performedalong the lines 26.

COMPARATIVE EXAMPLE

FIGS. 12( a) and (b) show an experimental result where a primarycleavage is performed for a wafer which has been fabricated as acomparative example. This comparative example has been fabricated by thesame method as the method described with respect to Embodiment 1 exceptthat the cleavage inducing members 3 are not formed.

FIG. 12( a) shows an upper face of the wafer of the comparative example.When a primary cleavage was performed in the direction of a line 25 inthe figure by using a cleavage apparatus, a crack occurred in the 60°direction with respect to the M-plane, and the laser bar 50 wasdisrupted part of the way, as shown in FIG. 12( b). As a result, only alaser bar 50 which is about ⅕ in length relative to the bar ofEmbodiment 1 was obtained, thus resulting in a very low yield. Moreover,the optical output end faces formed through primary cleavage are notflat, and therefore the operating current is high and the lifespan isshort.

Embodiment 2

Next, with reference to FIG. 13( a) to FIG. 13( i), a second embodimentof the nitride compound semiconductor laser according to the presentinvention will be described.

First, as shown in FIG. 13( a), a GaN wafer 1 whose upper face is the(0001) plane is provided, and a photoresist film 2 is applied on theupper face of the GaN wafer 1. The cross section of the GaN wafer 1 thatis shown in FIG. 13( a) to FIG. 13( i) is the M(1-100) plane, which willbe exposed through primary cleavage. The <11-20> direction lies in theplane of the figure, and is parallel to the upper face (0001) of the GaNwafer 1.

By subjecting the photoresist film 2 to exposure and development througha known photolithography step, the photoresist film 2 is patterned asshown in FIG. 13( b). The patterned photoresist film 2 has a pluralityof openings 2′ which are periodically arranged in a two-dimensionalmanner. The shapes, sizes, and positions of the openings 2′ can bearbitrarily set by changing the design of a photomask which is used forthe exposure in a photolithography step. In the present embodiment, thelocation of the openings 2′ is determined so as to define thearrangement of the cleavage inducing members 3 shown in FIG. 4.

Next, as shown in FIG. 13( c), a silicon dioxide film 3′ is deposited onthe photoresist mask 2. Although the silicon dioxide film 3 is mostlypositioned on the photoresist mask 2, some portions thereof are incontact with the upper face of the GaN wafer 1 through the openings 2′.Deposition of the silicon dioxide film 3′ may be performed by an ECRsputtering technique, for example.

Thereafter, a lift-off is performed by removing the photoresist film 2with an organic solution such as acetone, thus forming the cleavageinducing member 3 as shown in FIG. 13( d).

Next, after a GaN layer 4 is grown on the GaN wafer having the pluralityof cleavage inducing members 3 arranged on its upper face, the GaN wafer1 is taken out of the reactor, and an insulative film 5 for selectivegrowth is formed above the GaN layer 4. The insulative film 5 in thepresent embodiment is formed of SiO₂, with a thickness of about 100 nm,that has been deposited in a plasma CVD apparatus.

Next, after the resist film 6 is applied on the insulative film 5 in aphotolithography step, exposure and development is performed to form aresist film 6′ which is patterned in stripes, as shown in FIG. 13( f).The resist film 6′ is patterned so that each stripe has a width of 3 μm,with an arraying pitch of 18 μm. The stripes extend in a direction whichis parallel to the <1-100> direction of the GaN wafer 1.

Next, by using the resist film 6′ as an etching mask, the exposedportions of the insulative film 5 are removed with a hydrofluoric acidsolution, thus forming a stripe-shaped insulation mask 5′ as shown inFIG. 13( g). Thereafter, as shown in FIG. 13( h), the resist film 6′ isremoved with an organic solution such as acetone.

Next, in order to selectively grow a GaN layer 7, the substrate havingthe stripe-shaped insulative film 5′ deposited thereon is again retainedon a susceptor in a reactor of MOVPE equipment. Then the temperature iselevated to about 1000° C. in a hydrogen atmosphere at a pressure of 200Torr, and by using 7 sccm TMG and 7.5 slm NH₃ gas and simultaneouslysupplying a carrier gas of hydrogen, the GaN layer 7 is selectivelygrown on the selective growth mask pattern, as shown in FIG. 13( i).

The exposed portions of the GaN layer 4 function as seeds 9 of crystalgrowth. The dislocation density of the seeds 9 is equal to thedislocation density of the GaN wafer 1, and is about 1×10⁶/cm³. However,the dislocation density in the laterally-grown crystal region (wings) ofthe GaN layer 7 is reduced to about 1×10⁵/cm³.

Thereafter, by performing steps similar to the steps described withrespect to Embodiment 1, the semiconductor laser of the presentembodiment is fabricated. In the present embodiment, since the directionin which the optical waveguides 18 extend is made parallel to thedirection in which the stripe-shaped insulative film 5′ extends, theoptical waveguides 18 are formed in the selective growth regions havinga reduced dislocation density, so as to avoid the seeds 8 and thecrystal coupling portions 9 having a high dislocation density. As aresult, the operating current is reduced and the lifespan is extended.

According to the present embodiment, in addition to the effects ofEmbodiment 1, an effect of reducing the dislocation density in theselectively-grown layer is obtained, whereby the lifespan of the laserdevice is improved to 2000 hours or more.

Embodiment 3

Hereinafter, a third embodiment of the nitride compound semiconductorlaser according to the present invention will be described.

In the present embodiment, on the GaN wafer 1 before a nitride compoundsemiconductor crystal is grown thereon, trenches are periodically formedso as to be perpendicular to but not intersecting the opticalwaveguides, and mask layers (cleavage inducing members 3) are formed onthe trenches.

First, a resist film is deposited on the GaN wafer whose principal faceis the (0001) plane. By using a photolithography technique, the resistis removed in the form of dotted lines with an interval of about 400 μm,along the <11-20> direction of a subsequently-formed nitride compoundsemiconductor layer, so as to be perpendicular to but not intersectingthe optical waveguides. By using the resist film as an etching mask, theexposed portions of the GaN wafer are subjected to dry etching by usinga dry etching apparatus, and an array of a plurality of trenches 27 areformed on the upper face of the GaN wafer 1 as shown in FIG. 14. Eachtrench 27 is sized about 2 μm (longitudinal)×10 μm (lateral), with adepth of about 2 μm, and they are preferably formed in positions for notunfavorably affecting the neighborhood of the subsequently-formedoptical waveguides, e.g., crystal strain. The trenches 27 have a V-shapein any cross section parallel to the (11-20) plane. It is preferablethat the trenches 27 have a long extent along the <11-20> direction, andform an apex of an acute angle at its both ends.

Next, as shown in FIG. 15, cleavage inducing members 3 are formed in thetrenches 27. The method for forming the cleavage inducing members 3 issimilar to the method described with respect to Embodiment 1. However inthe present embodiment, it is preferable to carry out a high-precisionmask alignment so as to match the positions of the cleavage inducingmembers 3 with the positions of the trenches 27. However again, theremay be some offset between the cleavage inducing members 3 and thetrenches 27.

The subsequent steps are similar to the steps described with respect toEmbodiment 1, and the description thereof will not be repeated herein.

In the present embodiment, the trenches 27 are formed immediately underthe cleavage inducing members 3, so that cleavage is more likely to beinduced, and it is even easier to form smooth resonator end faces.

Embodiment 4

Hereinafter, a fourth embodiment of the nitride compound semiconductorlaser according to the present invention will be described.

In the present embodiment, as shown in FIG. 16, an n-type GaN wafer 1 isused and an n-type electrode 24 is formed on its rear face. In thepresent embodiment, after the optical waveguide 18 is formed, polishingis performed from the rear face of the GaN wafer 1 so as to attain anoverall thickness of about 70 μm. According to the conventional cleavagemethod, the mechanically fragile substrate has been prone to destructionwhen scribing and dicing are used, thus resulting in a low yield;therefore, it has been necessary to leave a substrate thickness of about100 μm in the polishing step. However, in the present embodiment, thesubstrate thickness can be made further thinner because scribing anddicing, etc., are not used. A thinner substrate leads to an increasedheat radiation efficiency of the entire laser device, so that an effectof increasing the laser device's lifespan is expected.

Since an electrically conductive n-type GaN wafer 1 is used in thepresent embodiment, it is possible to form the n-side electrodes 24directly on the rear face of the GaN wafer 1, as shown in FIG. 16.

Note that, if the n-side electrodes 24 are patterned so as to avoid theregions where primary cleavage and secondary cleavage are to occur,peeling of the n-side electrodes 24 during cleavage can be prevented.However, the n-side electrodes 24 may be formed over the entire rearface of the n-type GaN wafer 1.

In the present embodiment, since electrodes are formed on the rear faceof the GaN wafer 1, it is possible to reduce the size of the laserdevice, and the laser device can be produced at a low cost.

EXAMPLE

The shape and size of cleavage inducing members were changed in variousmanners, and soundness of cleavage was evaluated. Hereinafter, aproduction method for the samples used in the Example will be described.

First, a GaN wafer having a thickness of 400 μm was provided, andcleavage inducing members composed of an insulative film were formed onits principal face. Specifically, after cleaning the GaN wafer withacetone, solfine, methanol, and buffered hydrofluoric acid (BHF), an SiNlayer (lower layer) and an SiO₂ layer (upper layer) were sequentiallydeposited by using an ECR sputtering apparatus. The thicknesses of theSiO₂ layer and the SiN layer were respectively set at 10 nm and 100 nm,or 10 nm and 500 nm.

Next, this multilayer was patterned by a photolithography technique andan etching technique. Etching of the SiN layer and the SiO₂ layer wasperformed through a dry etching using CF₄ (carbon tetrafluoride) gas.Thereafter, cleaning (acetone+sulfuric acid/hydrogen peroxide) wasperformed to form cleavage inducing members of a desired shape. Thecleavage inducing members in the present Example function as mask layersfor the selective growth in an epitaxial growth step to be nextperformed. Hereinafter, the cleavage inducing members in the presentExample will be referred to as “mask layers”.

FIGS. 17( a) to (c) each shows a planar shape of a mask layer formed inthe present Example. FIGS. 17( a) and (b) show mask layers of ahexagonal planar shape, placed in a linear arrangement along the <11-20>direction. The angle between the <11-20> direction and a side having avertex pointed in the <11-20> direction at one end thereof is set at 30degrees in the example of FIGS. 17( a), and 60 degrees in the example ofFIG. 17( b). FIG. 17( c) shows a mask layer having a rectangular planarshape, linearly arranged along the <11-20> direction.

In each of the mask layers shown in FIGS. 17( a) and (c), the side whichis parallel to the <11-20> direction is relatively longer than the othersides.

Table 1 shows sizes for mask layers having the shape shown in FIG. 17(a) (sample Nos. 1 to 6). Table 2 shows sizes for mask layers having theshape shown in FIG. 17( b) (sample Nos. 7 to 12). Table 3 shows sizesfor mask layers having the shape shown in FIG. 17( c) (sample Nos. 13 to24). For each sample, the thickness of the mask layers was set to either100 nm or 500 nm, as mentioned earlier.

TABLE 1 Hexagonal (30 deg) <11-20> × <1-100> No. [μm] [μm] results 1  10× 5 [μm] ◯ 2  50 × 5 ◯ 3  50 × 10 ◯ 4 180 × 5 ◯ 5 180 × 10 ◯ 6 180 × 50◯

TABLE 2 Hexagonal (60 deg) <11-20> × <1-100> No. [μm] [μm] results 7 10× 5 ◯ 8 50 × 5 ◯ 9  50 × 10 ◯ 10 180 × 5  ◯ 11 180 × 10 ◯ 12 180 × 50 ◯

TABLE 3 Rectangular <11-20> × <1-100> No. [μm] [μm] results 13 3 × 5 X14  3 × 10 X 15 5 × 5 X 16 10 × 5  ◯ 17 10 × 10 ◯ 18 10 × 50 ◯ 19 50 ×5  ◯ 20 50 × 10 ◯ 21 50 × 50 ◯ 22 180 × 5  ◯ 23 180 × 10  ◯ 24 180 × 50 X

Note that each table shows the size along the <11-20> direction and thesize along the <1-100> direction of each mask layer. For example, insample No. 6 shown in Table 1, the mask layers have a size of 180 μmalong the <11-20> direction and a size of 50 μm along the <1-100>direction.

In the present Example, a large number of mask layers having theaforementioned shapes and sizes were arranged on a wafer with a pitch of400 μm. The number of mask layers arranged along a single line wasthirty.

Next, selective epitaxial growth of a nitride compound semiconductor wasperformed by an MOVPE technique. Specifically, the wafer was cleanedwith BHF, and SiO₂ on the mask layers was subjected to wet etching toallow a clean SiN mask surface to be exposed. Thereafter, semiconductormultilayer structure having a double-hetero structure was formed in anMOVPE reactor. The growth conditions were similar to the conditions ofthe growth performed when forming the semiconductor multilayer structure40 shown in FIG. 2( e).

In the present Example, the surface of the mask layers was composed ofSiN, and hardly any semiconductor layer grew on this surface. However,in the case of mask layers having a size of 5 μm or less, the upper faceof the mask layers was almost covered by the semiconductor layer due tolateral growth. The thickness of the semiconductor multilayer structurecovering the mask layers was not uniform, and depressions were formed onthe upper face due to the presence of the mask layers.

The wafer having the semiconductor multilayer structure thus formed onits principal face was polished from the rear face, and the waferthickness was adjusted to about 100 μm. Thereafter, cleavage wasperformed via edge scribing and breaking, and the soundness of cleavagewas evaluated.

The rightmost column in Table 1 to Table 3 show evaluation results ofsample Nos. 1 to 24. In the “results” column of each table, the “◯”symbol indicates that 12 mm-long bars were appropriately fabricatedthrough cleavage. On the other hand, the “X” symbol indicates that thecleavage planes deviated from the mask layer rows, so that 12 mm-longbars could not be appropriately fabricated.

In Samples 13 to 15 of Table 3, cleavage was not appropriatelyperformed. The reason is that the mask layer size was too small. FIG. 18is an optical micrograph showing a cross section of a sample whose masklayers had a small planar size, resulting in a cleavage plane deviatingfrom a mask layer row. As can be seen from FIG. 18, an end-face crack isformed at the cleavage plane. However, even if the mask layer size issmall, appropriate cleavage was realized in the case where mask layersof a hexagonal shape was used as shown in Table 1 and Table 2.

In the case where the mask layers had a rectangular shape, as shown inTable 3, cleavage was not properly performed when the size along the<1-100> direction was as large as 50 μm or more.

As can be seen from the above results, it is preferable that the masklayers are shaped so as to have a vertex pointing in a directionparallel to a cleavage plane. In the case of employing mask layers of ashape having no such vertices (e.g., rectangle or square), it ispreferable to set their size to be within an appropriate range.

FIG. 19 is an optical micrograph showing a cross section of a samplewhose mask layers have such a large planar size that the epitaxial layernear the mask layers has acquired a non-uniform thickness. If the masklayers become too large, strain and the like may occur in thesemiconductor multilayer structure. Therefore, the mask layers arepreferably formed so as to be smaller than 180 μm×50 μm in size, anddesirably smaller than 10m μm×30 μm in size. Moreover, the thickness ofthe mask layers may be set to an arbitrary value of 1.0 μm or less, forexample. Note that the mask layer(s) which remains in at least some ofthe four corners of the chip after cleavage will typically have a sizewhich is about half the aforementioned size.

FIG. 20 is an optical micrograph showing the principal face, aftercleavage, of a substrate of a sample on which mask layers of arelatively large size are formed. While the cleavage plane was deviatedfrom the mask layer row where the mask layers had a rectangular planarshape, appropriate cleavage occurred where the mask layers had ahexagonal planar shape.

As has been described above, according to the present invention,cleavage inducing members are arranged in intermittent and linearmanners on a wafer, whereby cleavage can be performed with a good yield.

As shown in FIG. 21( a), in the case where a trench 300, etc., thatextends long and continuously on a plane at which cleavage is to occuris formed on a wafer, the cleavage plane will deviate significantly fromthe direction in which the trench extends if the direction in which thetrench extends deviates even slightly from the easily-cleavage plane ofthe crystal, thus detracting from the purpose of providing the cleavageinducing members. On the other hand, in the case where the cleavageinducing members 3 are arranged in an intermittent manner as shown inFIG. 21( b), the cleavage plane is prevented from deviatingsignificantly from the direction along which the cleavage inducingmembers are arranged, even if there is a discrepancy between thedirection of their arrangement and the easily-cleavable direction.

Note that, by removing the mask layers through etching after finishingthe epitaxial growth step, gaps may be formed in the portions where themask layers existed. When cleavage is performed after such an etching,the gaps will function as cleavage inducing members.

INDUSTRIAL APPLICABILITY

As lasers for short-wavelength light sources employing GaN substrateswhich are difficult to be cleaved, mass production of nitride compoundsemiconductor lasers according to the present invention is expected.

1. A nitride compound semiconductor element including a substrate havingan upper face and a lower face and a semiconductor multilayer structuresupported by the upper face of the substrate, such that the substrateand the semiconductor multilayer structure have at least two cleavageplanes, comprising: at least one cleavage inducing member in contactwith one of the at least two cleavage planes, wherein a length of the atleast one cleavage inducing member along a direction parallel to the oneof the at least two cleavage planes is smaller than a length of theupper face of the substrate along the direction parallel to the one ofthe at least two cleavage planes, wherein the cleavage inducing memberis composed of a mask layer formed on the upper face of the substrate orin the semiconductor multilayer structure or composed of a gap which isformed in the semiconductor multilayer structure, and wherein thecleavage inducing member has a size smaller than a 180 μm×50 μmrectangle.
 2. The nitride compound semiconductor element of claim 1,wherein the upper face of the substrate has a rectangular shape, and thecleavage inducing member is positioned in at least one of four cornersof the upper face of the substrate.
 3. The nitride compoundsemiconductor element of claim 1, wherein, the semiconductor multilayerstructure has a laser resonator structure in which the two cleavageplanes function as resonator end faces; and a length of the at least onecleavage inducing member along a resonator length direction is half orless of the resonator length.
 4. The nitride compound semiconductorelement of claim 1, wherein, two or more cleavage inducing members arecomprised, and arranged along a resonator length direction; and aninterval between adjoining cleavage inducing members along the resonatorlength direction is 80% or more of the resonator length.
 5. The nitridecompound semiconductor element of claim 1, wherein a trench is formed onthe upper face of the substrate; and the mask layer is positioned abovethe trench.
 6. The nitride compound semiconductor element of claim 1,wherein the mask layer is composed of a material which suppressescrystal growth of semiconductor layers composing the semiconductormultilayer structure.
 7. The nitride compound semiconductor element ofclaim 1, wherein the mask layer is formed of at least one materialselected from the group consisting of: an oxide or nitride of silicon,aluminum, titanium, niobium, zirconia, or tantalum; gold; platinum;aluminum; nickel; palladium; and titanium.
 8. The nitride compoundsemiconductor element of claim 3, wherein the at least one cleavageinducing member is located on both sides of a laser optical waveguideportion in the semiconductor multilayer structure.
 9. The nitridecompound semiconductor element of claim 1, wherein the semiconductormultilayer structure includes: an n-type nitride compound semiconductorlayer and a p-type nitride compound semiconductor layer; and an activelayer interposed between the n-type nitride compound semiconductor layerand the p-type nitride compound semiconductor layer.
 10. The nitridecompound semiconductor element of claim 1, wherein the substrate is anitride compound semiconductor.
 11. The nitride compound semiconductorelement of claim 6, wherein a pair of electrodes are formed on the upperface and the lower face of the substrate.
 12. A production method for anitride compound semiconductor element including a substrate having anupper face and a lower face and a semiconductor multilayer structuresupported by the upper face of the substrate, comprising: a step ofproviding a wafer to be split into the substrate; a step of growingsemiconductor layers composing the semiconductor multilayer structure onthe wafer; and a step of performing cleavage of the wafer and thesemiconductor multilayer structure to form a cleavage plane of thesemiconductor multilayer structure, further comprising a step ofarranging a plurality of cleavage inducing members at positions wherethe cleavage plane is to be formed, wherein the cleavage inducing memberis composed of a mask layer formed on the upper face of the substrate orin the semiconductor multilayer structure or composed of a gap which isformed in the semiconductor multilayer structure, and wherein thecleavage inducing member has a size smaller than a 180 μm×50 μmrectangle.
 13. The production method of claim 12, wherein the step ofarranging the cleavage inducing members includes: a step of depositingan insulative film; and a step of patterning the insulative film to forma plurality of mask layers being arranged along a line and definingpositions at which the resonator end faces are to be formed.